1. Field of the Invention
The present Invention relates to an immersion type heat exchanger used in a state where it is immersed in a surface treatment bath in order to heat a liquid to be heated, and particularly to a heat exchanger which causes no separation of the fluororesin film coated thereon and no adhesion of sludge even if it is immersed in the treatment bath during use for a long time.
2. Description of the Related Art
When a metallic material is subjected to surface treatment by immersion in a phosphate solution, a metallic coil type heat exchanger, a plate heat exchanger or a laminated plate heat exchanger is generally used for heating the phosphate solution.
However, phosphate surface treatment has the problem that since the free iron produced in the solution adheres to the surface of the heat exchanger and is solidified into sludge with the passage of time, the thermal conduction efficiency of the surface of the heat exchanger deteriorates.
The work of removing the sludge which adheres to tile heat exchanger must thus be performed at intervals of 2 to 3 months, and the heat exchanger cannot be used during the removal work. Namely, there are not only the problem that surface treatment with a phosphate solution is impossible but also the problems that the work of removing sludge is a manual work and thus exhibits a low efficiency, and that it is increasingly difficult to secure the workers because the work is a physical work and makes dirty.
Although an attempt is made to coat a general fluororesin on the surface of the heat exchanger, the fluororesin is separated after use for about 1 to 1.5 months due to a large difference between the thermal expansion coefficients of the coated fluororesin and the surface material of the heat exchanger, and the coating effect thus deteriorates.